It's "occurrence", not "occurance". Your code may be the
greatest thing in the world since sliced bread, but if
routine names contain spelling mistakes people are going to
believe that the code contains other shoddinesses, thus
you wind up needlessly damaging your reputation.

Worse, client programmers using your code are going to
stumble and trip, because they're going to try and call
count_occurrences and fail miserably.